Dermatome Types for Skin Grafts: Humby, Watson and Silver Knives Explained

Humby, Watson and Silver are hand held skin graft knives, the manual form of the dermatome. Each one holds a long blade under a roller or guard whose gap sets how thick a split thickness graft will be. The Humby and the Watson are full size knives for large donor sites such as the thigh. The Watson is a later design with a firmer thickness adjustment. The Silver is a miniature knife for small grafts from areas a large knife cannot reach.

How did the hand held dermatome develop?

Split thickness grafts were first cut with long freehand knives, and the thickness depended entirely on the surgeon's hand. The Humby knife added an adjustable roller in front of the blade, so the gap between roller and blade sets the graft thickness. The history of the dermatome describes it as a Blair type knife with that roller added, and a Royal Australasian College of Surgeons history of freehand graft knives dates Humby's adjustable knife to the 1930s.

Later knives refined it. Braithwaite's knife of the 1950s modified the Humby, and the Watson knife of 1960 modified the Braithwaite with a smooth roller and a simpler, more rigid thickness control. That firmer control is the reason the Médecins Sans Frontières equipment catalogue lists the Watson as replacing the Humby. Drum dermatomes (Padgett, around 1940) and electric dermatomes (Brown, 1948) came alongside, but hand knives stayed in use because they are simple, need no power and can be sterilized like any other instrument.

How do the Humby, Watson and Silver differ?

The Humby and the Watson take the same spare blade, so a department can stock one blade for both.

Which dermatome should you choose?

• For large grafts from the thigh or the back, a Watson or a Humby. If your team learned on one, stay with it. Technique matters more than the brand of knife.
• For small grafts from places a long knife cannot sit flat, choose the Silver.
• For a burns or reconstructive unit, one full size knife plus one Silver covers most cases. Order spare blades with them.

How is the graft thickness set?

The adjustment changes the gap between the roller or guard and the blade edge. A common check is to hold the knife up to light and look at the gap along the full length of the blade: it should be even from end to end. An uneven gap gives a graft that is thicker on one side. Set and check the gap before every harvest, with a new blade fitted.

How should a graft knife be cleaned?

Remove the blade before cleaning, carefully, and discard single use blades in a sharps container. Clean the roller, the adjustment mechanism and the blade seat, where tissue collects, then dry fully before sterilizing. See our instrument care guide and the CDC guidance on cleaning instruments before sterilization.

Frequently asked questions

What is the difference between a Humby and a Watson knife?

Both are full size hand held graft knives with an adjustable roller. The Watson is a later design with a firmer thickness adjustment.

What is a Silver dermatome used for?

Small split thickness grafts from small or curved donor sites where a full size knife cannot sit flat.

Do Humby and Watson dermatomes use the same blade?

Ours do. One spare blade fits both.

Is a hand dermatome autoclavable?

Yes. Take the blade out, clean and dry the body, then autoclave it.

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Order graft knives and blades

See the skin grafting tools range. For a unit set with spare blades, send us your list and we will send you a quote.